Orbital implants have long been used to treat patients having an eviscerated or enucleated eye. It is further known that such treatment is enhanced by encouraging fibrovascular ingrowth into porous implants so that they may become integrated as disclosed in Perry, U.S. Pat. No. 6,063,117 incorporated herein by this reference.
Porous materials such as hydroxyapatite (“HA”) do have some drawbacks. Naturally derived HA exhibits surface spicules which can abrasively contact other structures within the orbit which can make insertion difficult. Further abrasion can occur after insertion, leading to the generally unwanted condition of exposure of the implant.
It has been found that a coating or wrapping of a smooth, sheet material on the outer surface of the porous core of the implant can provide a smooth surface which will facilitate deep insertion. The coating also provides a secure structure onto which the extraocular muscles may be sutured in close proximity to the implant in order to provide a good blood supply for encouraging rapid fibrovascular ingrowth. Unfortunately, such a coating can discourage rapid fibrovascular ingrowth by blocking access of bodily fluids and blood vessels to the porous core.
It is further shown in Perry, U.S. Pat. No. 6,248,130, incorporated herein by this reference, that a coating made of bioabsorbable sheet material will allow both easy insertion and, as it degrades, allow full integration with fibrovascular tissue. The materials selected for the coating should not cause an undue adverse immune response and, preferably, will be rapidly bioabsorbed or penetrated by the patient's body to allow integration with fibrovascular tissue. Preferably, the coating must be made from a material which is strong enough to securely hold sutures.
Various materials have been proposed from plaster of paris to biodegradable polymeric compounds such as polyglycolic acid (“PGA”), and polylactic acid (“PLA”) among others. Depending on various parameters such as its molecular morphology (crystalline vs. amorphous), hydrophobicity, and presence of additives, among others, such materials typically exhibit different rates of degradation in the body and will become bio-absorbed at different times.
This required manufacturers to weigh the benefits of a faster degrading coating which would encourage more rapid vascularization against the disadvantages of less secure muscle attachment over time, and the irritation caused by projecting spicules. Although slower degradation provides longer lasting smoothness, secure muscle attachment, and encourages epithelial cell growth if exposed, it discourages rapid fibrovascular ingrowth.
There is a need, therefore, to provide an implant which minimizes the above-described negative effects.